1. Field of the Invention
The present invention relates to glass mats, and more particularly, to glass fiber mats for application in roofing products such as asphalt shingles.
2. Prior Art
Asphalt roofing shingles are based on an interior web or carrier of a wet process glass fiber mat. Shingle manufacturing consists of running a continuous wet process glass fiber mat in a bath of molten asphalt to cause a coating on both sides of the mat as well as filling in the interstices between the individual glass fibers.
It is common in the art of manufacturing glass fiber mats, woven materials and other reinforcing materials to apply a binder to both assist in holding the reinforcing material together and promoting a better bond between a matrix resin and the reinforcing material during a subsequent RIM, RTM or SRIM molding process.
These binders are usually dry, powder resins, but can be emulsions or liquids. The fiber materials are produced in a conventional manner for the type of construction desired. Normally, the binders are applied to the reinforcements and then subjected to heating, to melt, or dry-before-melt, and sometimes to cure the binders. This process uses significant quantities of energy as the entire mass of reinforcing material needs to be heated to the required melting and/or drying and/or reaction temperatures. The binder can be unsaturated, cured or staged, depending on the application requirements.
Wet process glass fiber mats are conventionally made from glass fibers held together by a binder comprising a thermoplastic and thermoset polymer system. Typically, a binder is applied in a liquid form and dispersed onto the glass fibers through an applicator such as a curtain coater. Conventional wet processes strive to produce a uniform coating of binder on the glass fibers, and to produce a shingle with an even distribution of fibers. After the binder and glass fibers have been dried and cured in an oven, the glass fiber mat is gauged and cut as desired.
Unfortunately, such conventional binders are not always compatible with the asphalt used to coat the mats in asphaltic composites such as roofing shingles. This can cause processing difficulties, and can result in roofing shingles having poor tear strength and a loose coating.
Current technology for glass mat manufacturing process on commercially available Deltaformer™ formers produces a mat with variable properties, e.g., tensile strength properties in machine direction (MD) and cross machine direction (CMD), with MD tensile strength being higher than CMD tensile strength. Another problem that is frequently confronted in glass mat manufacturing process is basis weight variation across the CMD. This phenomenon is called sheet anisotropy. For a variety of reasons it would be desirable to provide glass mats having improved isotropy.
Shake mechanism has been used in pulp and paper industry and refers to a setup in which the forming wire in the wet-end section (also known as the wet forming section), which is located immediately after the headbox, is moved at some predetermined amplitude and frequency perpendicular to the machine direction (i.e., in the cross machine direction). In modern machines, this kind of movement is usually achieved by shaking the breast roll. The purpose of shaking the breast roll can improve the formation of the resulting fiber mat by redistribution of fibers from high concentration areas to low concentration areas and orient fibers in the cross machine direction. This movement of fibers is relatively easy, when they are in the fluidized state in the initial part of the forming section. Therefore, it is believed for this technology to produce positive results that it be applied on fibers which are in a state of flotation rather than being consolidated in the network structure, where their freedom to move around is restricted.
Shaking the breast roll has historically been done in the paper industry to produce an isotropic sheet with reduced basis weight variation. However, it has not been implemented in long glass fibers machines. Thus, it would be desirable to improve the quality of glass fiber mats to asphaltic composites such as shingles, and improve product performance in the areas of processing and tear strength.